The river has a total drainage area exceeding 1,165,000 km2 (450,000 sq mi). Its estimated annual flow stands at around 207 km3 (50 cu mi), making it the twenty-first largest river in the world in terms of annual flow. The Zanskar is its left bank tributary in Ladakh. In the plains, its left bank tributary is the Chenab which itself has four major tributaries, namely, the Jhelum, the Ravi, the Beas and the Sutlej. Its principal right bank tributaries are the Shyok, the Gilgit, the Kabul, the Gomal and the Kurram. Beginning in a mountain spring and fed with glaciers and rivers in the Himalayas, the river supports ecosystems of temperate forests, plains and arid countryside.

The word "Indus" is the romanised form of the ancient Greek word "Indós" (Ἰνδός), borrowed from the old Persian word "Hinduš", which in turn was derived from the Sanskrit word "Sindhu" (सिन्धु pronounced [sɪndʱuː]).[1] The word "Sindhu" or "Sindh" is still the local appellation of the Indus River. The original Sanskrit word "Sindhu" is an amalgamation of two words, "sim" (region or entirety or border) and "dhu" (to tremble or shake) and means "a body of trembling water, river, stream or ocean".

Rigveda also describes several mythical rivers, including one named "Sindhu". The Rigvedic "Sindhu" is thought to be the present-day Indus river and is attested 176 times in its text – 95 times in the plural, more often used in the generic meaning. In the Rigveda, notably in the later hymns, the meaning of the word is narrowed to refer to the Indus river in particular, as in the list of rivers mentioned in the hymn of Nadistuti sukta. The Rigvedic hymns apply a feminine gender to all the rivers mentioned therein but "Sindhu" is the only river attributed with a masculine gender. Sindhu is seen as a strong warrior amongst other rivers which are seen as goddesses and compared to cows and mares yielding milk and butter.

In Urdu, the official language of Pakistan, the Indus is known as درياۓ سِندھ(Daryā-e Sindh). In other languages of the region, the river is known as सिन्धु नदी (Sindhu Nadī) in Hindi, سنڌو (Sindhu) in Sindhi, سندھ(Sindh) in Shahmukhi alphabet, ਸਿੰਧ ਨਦੀ (Sindh Nadī) in Gurmukhī alphabet, સિંધ��� નદી (Sindhu) in Gujarati; اباسين (Abāsin, lit. "Father of Rivers") in Pashto, رود سند (Rūd-e Sind) in Persian, نهر السند (Nahar al-Sind) in Arabic, སེང་གེ།་གཙང་པོ (Sênggê Zangbo, lit. "Lion River") in Tibetan, 印度 (Yìndù) in Chinese, and Nilab in Turki.

The Indus River provides key water resources for Pakistan's economy – especially the breadbasket of Punjab province, which accounts for most of the nation's agricultural production, and Sindh. The word Punjab means "land of five rivers" and the five rivers are Jhelum, Chenab, Ravi, Beas and Sutlej, all of which finally flow into the Indus. The Indus also supports many heavy industries and provides the main supply of potable water in Pakistan.

The ultimate source of the Indus is in Tibet; the river begins at the confluence of the Sengge and Gar rivers that drain the Nganglong Kangri and Gangdise Shan (Gang Rinpoche, Mt. Kailas) mountain ranges. The Indus then flows northwest through Ladakh and Baltistan into Gilgit, just south of the Karakoram range. The Shyok, Shigar and Gilgit rivers carry glacial waters into the main river. It gradually bends to the south, coming out of the hills between Peshawar and Rawalpindi. The Indus passes gigantic gorges 4,500–5,200 metres (15,000–17,000 feet) deep near the Nanga Parbatmassif. It flows swiftly across Hazara and is dammed at the Tarbela Reservoir. The Kabul River joins it near Attock. The remainder of its route to the sea is in the plains of the Punjab and Sindh, where the flow of the river becomes slow and highly braided. It is joined by the Panjnad at Mithankot. Beyond this confluence, the river, at one time, was named the Satnad River (sat = "seven", nadī = "river"), as the river now carried the waters of the Kabul River, the Indus River and the five Punjab rivers. Passing by Jamshoro, it ends in a large delta to the east of Thatta.

The Indus is one of the few rivers in the world to exhibit a tidal bore. The Indus system is largely fed by the snows and glaciers of the Himalayas, Karakoram and the Hindu Kush ranges of Tibet, the Indian states of Jammu and Kashmir and Himachal Pradesh and the Northern Areas of Pakistan. The flow of the river is also determined by the seasons – it diminishes greatly in the winter, while flooding its banks in the monsoon months from July to September. There is also evidence of a steady shift in the course of the river since prehistoric times – it deviated westwards from flowing into the Rann of Kutch and adjoining Banni grasslands after the 1816 earthquake.[3][4]

The traditional source of the river is the Senge Khabab or "Lion's Mouth", a perennial spring, not far from the sacred Mount Kailash marked by a long low line of Tibetan chortens. There are several other tributaries nearby, which may possibly form a longer stream than Senge Khabab, but unlike the Senger Khabab, are all dependent on snowmelt. The Zanskar River, which flows into the Indus in Ladakh, has a greater volume of water than the Indus itself before that point.[5]

"That night in the tent [next to Senge Khabab] I ask Sonmatering which of the Indus tributaries which we crossed this morning is the longest. All of them, he says, start at least a day's walk away from here. The Bukhar begins near the village of Yagra. The Lamolasay's source is in a holy place: there is a monastery there. The Dorjungla is a very difficult and long walk, three days perhaps, and there are many sharp rocks; but it its water is clear and blue, hence the tributary's other name, Zom-chu, which Karma Lama translates as 'Blue Water'. The Rakmajang rises from a dark lake called the Black Sea.

One of the longest tributaries — and thus a candidate for the river's technical source — is the Kla-chu, the river we crossed yesterday by bridge. Also known as the Lungdep Chu, it flows into the Indus from the south-east, and rises a day's walk from Darchen. But Sonamtering insists that the Dorjungla is the longest of the 'three types of water' that fall into the Seng Tsanplo ['Lion River' or Indus]."[5]

The major cities of the Indus Valley Civilization, such as Harappa and Mohenjo-daro, date back to around 3300 BC, and represent some of the largest human habitations of the ancient world. The Indus Valley Civilization extended from across Pakistan and northwest India, with an upward reach from east of Jhelum River to Ropar on the upper Sutlej. The coastal settlements extended from Sutkagan Dor at the Pakistan, Iran border to Kutch in modern Gujarat, India. There is an Indus site on the Amu Darya at Shortughai in northern Afghanistan, and the Indus site Alamgirpur at the Hindon River is located only 28 km (17 mi) from Delhi. To date, over 1,052 cities and settlements have been found, mainly in the general region of the Ghaggar-Hakra River and its tributaries. Among the settlements were the major urban centers of Harappa and Mohenjo-daro, as well as Lothal, Dholavira, Ganeriwala, and Rakhigarhi. Only 90–96 of more than 800 known Indus Valley sites have been discovered on the Indus and its tributaries.[citation needed] The Sutlej, now a tributary of the Indus, in Harappan times flowed into the Ghaggar-Hakra River, in the watershed of which were more Harappan sites than along the Indus.

The word "India" is derived from the Indus River. In ancient times, "India" initially referred to those regions immediately along the east bank of the Indus, but by 300 BC, Greek writers including Megasthenes were applying the term to the entire subcontinent that extends much farther eastward.[6]

Confluence of Indus and Zanskar rivers. The Indus is at the bottom of the picture, flowing left-to-right; the Zanskar, carrying more water, comes in from the middle left of the picture.

The Indus river feeds the Indus submarine fan, which is the second largest sediment body on the Earth at around 5 million cubic kilometres of material eroded from the mountains. Studies of the sediment in the modern river indicate that the Karakoram Mountains in northern Pakistan and India are the single most important source of material, with the Himalayas providing the next largest contribution, mostly via the large rivers of the Punjab (Jhelum, Ravi, Chenab, Beas and Sutlej). Analysis of sediments from the Arabian Sea has demonstrated that prior to five million years ago the Indus was not connected to these Punjab rivers which instead flowed east into the Ganges and were captured after that time.[7] Earlier work showed that sand and silt from western Tibet was reaching the Arabian Sea by 45 million years ago, implying the existence of an ancient Indus River by that time.[8] The delta of this proto-Indus river has subsequently been found in the Katawaz Basin, on the Afghan-Pakistan border.

In the Nanga Parbat region, the massive amounts of erosion due to the Indus river following the capture and rerouting through that area is thought to bring middle and lower crustal rocks to the surface.[9]

Accounts of the Indus valley from the times of Alexander's campaign indicate a healthy forest cover in the region, which has now considerably receded. The Mughal Emperor Babur writes of encountering rhinoceroses along its bank in his memoirs (the Baburnama). Extensive deforestation and human interference in the ecology of the Shivalik Hills has led to a marked deterioration in vegetation and growing conditions. The Indus valley regions are arid with poor vegetation. Agriculture is sustained largely due to irrigation works. Indus river and its watershed has a rich biodiversity. It is home to around 25 amphibian species and 147 species, 22 of which are only found in the Indus.[10]

The blind Indus River Dolphin (Platanista indicus minor) is a sub-species of dolphin found only in the Indus River. It formerly also occurred in the tributaries of the Indus river. According to the World Wildlife Fund claims it is one of the most threatened cetaceans with only about 1000 still existing.[11]

Palla fish Tenualosa ilisha of the river is a delicacy for people living along the river. The population of fish in the river is moderately high, with Sukkur, Thatta and Kotri being the major fishing centres – all in the lower Sindh course. But damming and irrigation has made fish farming an important economic activity. Located southeast of Karachi, the large delta has been recognised by conservationists as one of the world's most important ecological regions. Here the river turns into many marshes, streams and creeks and meets the sea at shallow levels. Here marine fishes are found in abundance, including pomfret and prawns.

The Indus is the most important supplier of water resources to the Punjab and Sindh plains – it forms the backbone of agriculture and food production in Pakistan. The river is especially critical since rainfall is meager in the lower Indus valley. Irrigation canals were first built by the people of the Indus valley civilization[citation needed], and later by the engineers of the Kushan Empire and the Mughal Empire. Modern irrigation was introduced by the British East India Company in 1850 – the construction of modern canals accompanied with the restoration of old canals. The British supervised the construction of one of the most complex irrigation networks in the world. The Guddu Barrage is 1,350 m (4,430 ft) long – irrigating Sukkur, Jacobabad, Larkana and Kalat. The Sukkur Barrage serves over 20,000 km2 (7,700 sq mi).

After Pakistan came into existence, a water control treaty signed between India and Pakistan in 1960 guaranteed that Pakistan would receive water from the Indus River and its two tributaries the Jhelum River & the Chenab River independently of upstream control by India.[12]

The Indus Basin Project consisted primarily of the construction of two main dams, the Mangla Dam built on the Jhelum River and the Tarbela Dam constructed on the Indus River, together with their subsidiary dams.[13] The Pakistan Water and Power Development Authority undertook the construction of the Chashma-Jhelum link canal – linking the waters of the Indus and Jhelum rivers – extending water supplies to the regions of Bahawalpur and Multan. Pakistan constructed the Tarbela Dam near Rawalpindi – standing 2,743 metres (9,000 ft) long and 143 metres (470 ft) high, with an 80-kilometre (50 mi) long reservoir. The Kotri Barrage near Hyderabad is 915 metres (3,000 ft) long and provides additional supplies for Karachi. It support the Chashma barrage near Dera Ismail Khan use for irrigation and flood control. for The Taunsa Barrage near Dera Ghazi Khan produces 100,000 kilowatts of electricity. The extensive linking of tributaries with the Indus has helped spread water resources to the valley of Peshawar, in the Khyber Pakhtunkhwa. The extensive irrigation and dam projects provide the basis for Pakistan's large production of crops such as cotton, sugarcane and wheat. The dams also generate electricity for heavy industries and urban centres.

The inhabitants of the regions through which the Indus river passes and forms a major natural feature and resource are diverse in ethnicity, religion, national and linguistic backgrounds. On the northern course of the river in the state of Jammu and Kashmir in India, live the Buddhist people of Ladakh, of Tibetan stock, and the Dards of Indo-Aryan or Dardic stock and practising Buddhism and Islam. Then it descends into Baltistan, northern Pakistan passing the main Balti city of Skardu. On its course river from Dubair Bala also drains into it at Dubair Bazar. People living at this area are mainly Kohistani and speak Kohistani language. Major areas through which Indus river pass through in Kohistan are Dasu, Pattan and Dubair. As it continues through Pakistan, the Indus river forms a distinctive boundary of ethnicity and cultures – upon the western banks the population is largely Pashtun, Baloch, and of other Iranian stock, with close cultural, economic and ethnic ties to eastern Afghanistan. The eastern banks are largely populated by people of Indo-Aryan stock, such as the Punjabis and the Sindhis. In northern Punjab and the Khyber Pakhtunkhwa, ethnic Pashtun tribes live alongside Dardic people in the hills (Khowar, Kalash, Shina, etc.), Burushos (in Hunza), and Punjabi people.

Through its course in Punjab the people living along the Indus river are distinct from Punjabi and Pustoon. This distinction is not only based on language (Saraiki dialect) but these people also have a different genealogy. They are tall and slender, distinctively different from either pushtoon or Punjabi which have a sturdy built. These people live in Mianwali and Dera Ismail Khan, Dera Ghazi Khan, Rahim Yar Khan and Rajan Pur in Punjab. In the province of Sindh, upper third of River indus is again inhabited by Saraiki speaking people up to Shikapur. The rest of the indus river valley is inhabited by Sindhis and Baloch of Sindhi language. Upon the western banks of the river live the Baloch and Pashtun people of Balochistan.

Satellite images of the upper Indus River valley, comparing water-levels on 1 August 2009 (top) and 31 July 2010 (bottom)

The Indus is a strategically vital resource for Pakistan's economy and society. After Pakistan and India declared Independence from the British Raj, also known as Indian Empire, the use of the waters of the Indus and its five eastern tributaries became a major dispute between India and Pakistan. The irrigation canals of the Sutlej valley and the Bari Doab were split – with the canals lying primarily in Pakistan and the headwork dams in India disrupting supply in some parts of Pakistan. The concern over India building large dams over various Punjab rivers that could undercut the supply flowing to Pakistan, as well as the possibility that India could divert rivers in the time of war, caused political consternation in Pakistan. Holding diplomatic talks brokered by the World Bank, India and Pakistan signed the Indus Waters Treaty in 1960. The treaty gave India control of the three easternmost rivers of the Punjab, the Sutlej, the Beas and the Ravi, while Pakistan gained control of the three western rivers, the Jhelum, the Chenab and the Indus. India retained the right to use of the western rivers for non-irrigation projects. (See discussion regarding a recent dispute about a hydroelectric project on the Chenab (not Indus) known as the Baglihar Project).

There are concerns that extensive deforestation, industrial pollution and global warming are affecting the vegetation and wildlife of the Indus delta, while affecting agricultural production as well. There are also concerns that the Indus river may be shifting its course westwards – although the progression spans centuries. On numerous occasions, sediment clogging owing to poor maintenance of canals has affected agricultural production and vegetation. In addition, extreme heat has caused water to evaporate, leaving salt deposits that render lands useless for cultivation.

Recently, India's construction of dams on the river, which Pakistan claims is in violation of the Indus Waters Treaty reducing water flow into Pakistan, has caused Pakistan to take the issue to the international courts for arbitration.

The Tibetan Plateau contains the world's third-largest store of ice. Qin Dahe, the former head of the China Meteorological Administration, said the recent fast pace of melting and warmer temperatures will be good for agriculture and tourism in the short term, but issued a strong warning:

"Temperatures are rising four times faster than elsewhere in China, and the Tibetan glaciers are retreating at a higher speed than in any other part of the world... In the short term, this will cause lakes to expand and bring floods and mudflows.. In the long run, the glaciers are vital lifelines of the Indus River. Once they vanish, water supplies in Pakistan will be in peril."[14]

"There is insufficient data to say what will happen to the Indus," says David Grey, the World Bank's senior water advisor in South Asia. "But we all have very nasty fears that the flows of the Indus could be severely, severely affected by glacier melt as a consequence of climate change," and reduced by perhaps as much as 50 percent. "Now what does that mean to a population that lives in a desert [where], without the river, there would be no life? I don't know the answer to that question," he says. "But we need to be concerned about that. Deeply, deeply concerned."[15]

In July 2010, following abnormally heavy monsoon rains, the Indus River rose above its banks and started flooding. The rain continued for the next two months, devastating large areas of Pakistan. In Sindh, the Indus burst its banks near Sukkur on 8 August, submerging the village of Mor Khan Jatoi.[20] In early August, the heaviest flooding moved southward along the Indus River from severely affected northern regions toward western Punjab, where at least 1,400,000 acres (570,000 ha) of cropland was destroyed, and the southern province of Sindh.[21] As of September 2010[update], over two thousand people had died and over a million homes had been destroyed since the flooding began.[22][23]

The 2011 Sindh floods began during the Pakistani monsoon season in mid-August 2011, resulting from heavy monsoon rains in Sindh, eastern Balochistan, and southern Punjab.[24] The floods caused considerable damage; an estimated 434 civilians were killed, with 5.3 million people and 1,524,773 homes affected.[25] Sindh is a fertile region and often called the "breadbasket" of the country; the damage and toll of the floods on the local agrarian economy was said to be extensive. At least 1.7 million acres (690,000 ha; 2,700 sq mi) of arable land were inundated. The flooding followed the previous year's floods, which devastated a large part of the country.[25] Unprecedented torrential monsoon rains caused severe flooding in 16 districts of Sindh.[26]

^Clift, Peter D.; Blusztajn, Jerzy (15 December 2005). "Reorganization of the western Himalayan river system after five million years ago". Nature438 (7070): 1001–1003. doi:10.1038/nature04379. PMID16355221.